Scientists from the University of Edinburgh discovered chemicals that prompt feelings of coolness had a dramatic painkiller effect.

The researchers, writing in the journal Current Biology, found the cooling compounds activated a protein called TRMP8.

They said their findings could form the basis of new treatments for people suffering from chronic pain conditions.

This careful chemical-induced cooling can give pain relief to people with chronic pain

Professor Susan Fleetwood-Walker

Chronic pain is continuous, long-term pain, which can be caused by diseases like arthritis or by nerve damage.

It affects millions of people worldwide and can be difficult to treat because of the long period that medication is required and possible drug side-effects.

Lead researcher Susan Fleetwood-Walker, professor of pain biology at the Centre for Neuroscience Research, Edinburgh University, said: "We are crying out for new treatments. Chronic pain can have an awful effect on a person's life quality."

Professor Fleetwood-Walker and colleagues investigated the analgesic qualities of a chemical called icilin, which is related to menthol.

Historical records show that cooling was used for pain relief in Ancient Greece, and other traditional remedies also employ cooling substances like mint oil to treat pain.

Chemical-induced cooling

The researchers looked at rats with chronic pain localised in one of their feet.

They found that when the rats were given icilin, either injected or rubbed onto the area where they were experiencing pain, they were able to withstand pressure to their paw, indicating the compound had had a painkilling effect.

The researchers discovered the chemical was activating a protein called TRPM8, which is expressed in the nerve cells in the skin and mediates the sensation of coolness.

Professor Fleetwood-Walker said: "We have found that if you can selectively activate the TRPM8 receptor, then you have a chance of suppressing other sensory inputs coming into the nervous system that are carrying pain information."

Small concentrations

She said she believed icilin will work on people with chronic pain, and should go into clinical trials, but better, more selective agents will probably need to be the developed in the future.

She said: "We found a very specific mechanism which means that this careful chemical-induced cooling can give pain relief to people with chronic pain - it does not affect normal pain.

"One of the exciting things about icilin is that it can be used in minute concentrations and it is sufficient to just paint it on the surface of the skin where the pain is to cause a painkilling effect that could last for hours afterwards.

Dr George Harrison, a chronic pain clinician and a spokesman for the British Pain Society, said: "Treatment of chronic pain is a major problem, and this research is very interesting and exciting.

"However, we need to see how we can translate this into putting drugs in place that are actually going to be effective at utilising this particular technique."

Professor Christopher Eccleston, director of the Bath Pain Management Unit at Bath University, said: "The team have highlighted the plight of a significant number of people who suffer unremitting and persistent pain.

"In isolating what appears a novel possible mechanism of analgesia the researchers have opened the door for new developments in non-opioid analgesics."